package org.apache.lucene.util;

import java.io.IOException;
import java.util.Map;

/**
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You under the Apache License, Version 2.0
 * (the "License"); you may not use this file except in compliance with
 * the License.  You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

/**
 * A utility for executing 2-phase commit on several objects.
 * 
 * @see TwoPhaseCommit
 * @lucene.experimental
 */
public final class TwoPhaseCommitTool {

    /**
     * A wrapper of a {@link TwoPhaseCommit}, which delegates all calls to the
     * wrapped object, passing the specified commitData. This object is useful for
     * use with {@link TwoPhaseCommitTool#execute(TwoPhaseCommit...)} if one would
     * like to store commitData as part of the commit.
     */
    public static final class TwoPhaseCommitWrapper implements TwoPhaseCommit {

        private final TwoPhaseCommit tpc;
        private final Map<String, String> commitData;

        public TwoPhaseCommitWrapper(TwoPhaseCommit tpc, Map<String, String> commitData) {
            this.tpc = tpc;
            this.commitData = commitData;
        }

        public void prepareCommit() throws IOException {
            prepareCommit(commitData);
        }

        public void prepareCommit(Map<String, String> commitData) throws IOException {
            tpc.prepareCommit(this.commitData);
        }

        public void commit() throws IOException {
            commit(commitData);
        }

        public void commit(Map<String, String> commitData) throws IOException {
            tpc.commit(this.commitData);
        }

        public void rollback() throws IOException {
            tpc.rollback();
        }
    }

    /**
     * Thrown by {@link TwoPhaseCommitTool#execute(TwoPhaseCommit...)} when an
     * object fails to prepareCommit().
     */
    public static class PrepareCommitFailException extends IOException {

        public PrepareCommitFailException(Throwable cause, TwoPhaseCommit obj) {
            super("prepareCommit() failed on " + obj);
            initCause(cause);
        }

    }

    /**
     * Thrown by {@link TwoPhaseCommitTool#execute(TwoPhaseCommit...)} when an
     * object fails to commit().
     */
    public static class CommitFailException extends IOException {

        public CommitFailException(Throwable cause, TwoPhaseCommit obj) {
            super("commit() failed on " + obj);
            initCause(cause);
        }

    }

    /** rollback all objects, discarding any exceptions that occur. */
    private static void rollback(TwoPhaseCommit... objects) {
        for (TwoPhaseCommit tpc : objects) {
            // ignore any exception that occurs during rollback - we want to ensure
            // all objects are rolled-back.
            if (tpc != null) {
                try {
                    tpc.rollback();
                } catch (Throwable t) {
                }
            }
        }
    }

    /**
     * Executes a 2-phase commit algorithm by first
     * {@link TwoPhaseCommit#prepareCommit()} all objects and only if all succeed,
     * it proceeds with {@link TwoPhaseCommit#commit()}. If any of the objects
     * fail on either the preparation or actual commit, it terminates and
     * {@link TwoPhaseCommit#rollback()} all of them.
     * <p>
     * <b>NOTE:</b> it may happen that an object fails to commit, after few have
     * already successfully committed. This tool will still issue a rollback
     * instruction on them as well, but depending on the implementation, it may
     * not have any effect.
     * <p>
     * <b>NOTE:</b> if any of the objects are {@code null}, this method simply
     * skips over them.
     * 
     * @throws PrepareCommitFailException
     *           if any of the objects fail to
     *           {@link TwoPhaseCommit#prepareCommit()}
     * @throws CommitFailException
     *           if any of the objects fail to {@link TwoPhaseCommit#commit()}
     */
    public static void execute(TwoPhaseCommit... objects) throws PrepareCommitFailException, CommitFailException {
        TwoPhaseCommit tpc = null;
        try {
            // first, all should successfully prepareCommit()
            for (int i = 0; i < objects.length; i++) {
                tpc = objects[i];
                if (tpc != null) {
                    tpc.prepareCommit();
                }
            }
        } catch (Throwable t) {
            // first object that fails results in rollback all of them and
            // throwing an exception.
            rollback(objects);
            throw new PrepareCommitFailException(t, tpc);
        }

        // If all successfully prepareCommit(), attempt the actual commit()
        try {
            for (int i = 0; i < objects.length; i++) {
                tpc = objects[i];
                if (tpc != null) {
                    tpc.commit();
                }
            }
        } catch (Throwable t) {
            // first object that fails results in rollback all of them and
            // throwing an exception.
            rollback(objects);
            throw new CommitFailException(t, tpc);
        }
    }

}
